Human leukocyte antigen (HLA) class I molecules have profound influences on infectious disease and cancer outcomes, via effects on immunity mediated by CD8+ T cells and natural killer (NK) cells. Three sets of genes, HLA-A, HLA-B and HLA-C encode HLA class I proteins. These genes are among the most polymorphic of human genes, with thousands of alleles found in humans. Each allotype presents a unique set of peptides at the cell surface, and individual peptides in complex with HLA class I molecules confer exquisite specificity for recognition by T cell receptors (TCR) of CD8+ T cells. In the canonical textbook-defined HLA class I assembly pathway, peptides that bind to HLA class I molecules are typically derived from the cytoplasm of cells, and transported into the endoplasmic reticulum (ER) by the transporter associated with antigen processing (TAP). In the ER, peptides assemble with HLA class I molecules in a process that is guided by specific assembly factors such as tapasin and generic ER chaperones. Peptide-loaded versions of HLA class I molecules exit the ER, whereas ER quality control is thought to retrieve peptide-deficient HLA class I for degradation, due to their relative instability. A number of our recent findings indicate that the canonical assembly pathway does not fully account for cell surface expression patterns of HLA-B allotypes in all cells, and additionally that peptide- deficient (empty) HLA-B do exist at the cell surface under some conditions, and are functional in the immune response. Based on these findings, it is our central hypothesis that HLA-B allotypes are functionally separable based on the stabilities of their empty forms and their peptide-binding preferences, and that these characteristics determine their competence for non-canonical assembly pathways and related functions. To test this hypothesis, we examine the model that HLA-B allotypes vary both in their constitutive cell surface expression levels and in cross-presentation efficiencies in antigen presenting cells (APC), based on competence for non-canonical assembly. We also examine the model that HLA-B allotypes vary in their abilities to induce effective CD8+ T cell immunity against Epstein Barr Virus (EBV) infections due to varying competencies for assembly in a TAP-deficient environment. Finally, the models of differential induction and novel functions for empty HLA-B in CD8+ T cell and NK cell functions are examined. Together, these studies address the central idea that the extreme polymorphisms of the HLA-B locus, which are evolutionarily-selected mutations within a confined region of the HLA class I structure, generate a hierarchy of protein folding and assembly phenotypes that are exploited by distinct arms of the immune response to maintain multi- compartmental and multimodal surveillance. These studies are expected to guide our progress in precision medicine by identifying best candidate HLA-B for specific vaccine targets, and provide new targets for combatting HLA-B-driven autoimmunity and drug hypersensitivity.

Public Health Relevance

HLA class I proteins play a key role in the immune system's ability to recognize and kill diseased cells. Thousands of HLA class I variants are present in human populations, but each person makes only up to six of the variants. A better knowledge of how HLA class I variants differ in their properties is important towards our understanding of why different people respond differently to the same disease and why some people have better immunity to disease. Additionally, a better grasp of HLA class I subgroup behaviors can lead to improved vaccine design and more personalized targeting of cancers, viral infections and autoimmune diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI044115-21
Application #
10106547
Study Section
Cellular and Molecular Immunology - A Study Section (CMIA)
Program Officer
Gondre-Lewis, Timothy A
Project Start
1999-01-15
Project End
2024-01-31
Budget Start
2021-02-01
Budget End
2022-01-31
Support Year
21
Fiscal Year
2021
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
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Geng, Jie; Altman, John D; Krishnakumar, Sujatha et al. (2018) Empty conformers of HLA-B preferentially bind CD8 and regulate CD8+ T cell function. Elife 7:
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Raghavan, Malini; Wijeyesakere, Sanjeeva J; Peters, Larry Robert et al. (2013) Calreticulin in the immune system: ins and outs. Trends Immunol 34:13-21

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